1. Field of the Invention
The invention relates to vehicles powered and steered by pumps. More particularly, the invention relates to an improved pump control linkage assembly for a pump driven vehicle such as a lawnmower.
2. Discussion of the Related Art
Vehicles equipped with hydraulically-powered drive systems that propel the drive wheels of a vehicle are generally known and are common and include, but are not limited to, walk behind lawnmowers, stand-on lawnmowers, and riding lawnmowers. Turning is typically achieved or at least facilitated by driving each drive wheel at different speeds. In some vehicles, they can even be turned in different directions at equal speeds for a very sharp or even a “zero-turn” radius, where the vehicle pivots about the midpoint of drive wheel axis. This kind of drive wheel steering system is more maneuverable than traditional vehicle steering systems that do not vary the relative speed of the drive wheels or that do not counter-rotate the drive wheels.
Hydraulically-powered drive systems typically include a separate variable displacement hydraulic pump for each of the drive wheels. Each variable displacement pump is typically an axial-piston type pump which includes a tilting internal swash plate which can be manipulated by an external lever to vary the pump discharge rate from a zero flow, also referred to as neutral, up to a maximum flow or reverse direction flow to a particular maximum. Such pumps are controlled by an operator controlled steering mechanism. The steering mechanism, sometimes taking the form of a pair of pivoting levers, is usually coupled to each of the pumps by a dedicated pump control linkage assembly configured to independently control the displacement of the pumps on either side of the vehicle. In this type of system, each steering lever is movable either forwardly or rearwardly from a center, neutral position to adjust the pump position for corresponding forward or reward driving.
Adjustment of the effective length of the pump linkage assembly is sometimes necessary to properly calibrate the linkage assembly with respect to the pump. For instance, during assembly of the vehicle, the linkage assembly length may be improperly set. Further, during operation, the linkage assembly may be jostled and otherwise disturbed so as to cause the linkage assembly length to be affected. The neutral position of the pump swash plate may also vary slightly over time. As such, the pumps of the vehicle may become uncentered such that, when the lever is positioned in neutral, the vehicle may experience a certain amount of unwanted forward or backward creep.
Traditional linkage assemblies of this type generally comprise a conventional turnbuckle located beneath the operator's seat and accessible by tilting the seat upwardly and forwardly. Each turnbuckle generally has an upper end connected to the control lever and a lower end connected to a pump swash plate and a rod disposed therebetween. A pair of jamb nuts or other such fasteners are typically employed to hold the turnbuckle assemblies in place. To adjust the linkage assembly length in such systems, both of the jamb nuts must be loosened and the rod itself must be turned to either extend or reduce the distance between the turnbuckle and the ends. This adjustment method can be quite difficult in operation because the lower end of the turnbuckle and even the rod can be very difficult to access because they are obstructed by the frame, the seat, and other components of the lawnmower.
The need therefore exists to provide a pump control, linkage assembly for a pump-driven vehicle that is easy to assembly, simple to maintain, and is robust enough to withstand the rigors associated with operation of such systems.
The need also exists for a pump control linkage assembly that can be quickly and efficiently assembled and maintained.